where \(E/N\)  takes model-dependent values (\(E\)  and \(N\)  denote the model-dependent anomalous electromagnetic and strong contributions). This coupling
is being explored by a plethora of experiments, as illustrated in Fig. REF .
For reference,
predictions of the benchmark \(Z_{\cal N}\) -KSVZ axion model [1]} are depicted for \(E/N=0\) .
The conclusion is that, for a large range of values of \({\cal N}\) , an axion-photon signal can be expected in large portions of the parameter space of upcoming axion DM experiments, if the \(Z_{\cal N}\)  axion accounts for the entire DM relic density.
<FIGURE>